3. Impulse Sound Sources
123
resulting in perhaps the largest and most complex nose in the animal
kingdom (Cranford 1999). These facts have caused some misconceptions
and controversy in the attempts to understand sound generation by comparing the anatomic relationships between nasal apparatuses in physeterid
and nonphyseterid odontocetes. The interpretation of these homologous
relationships (between nasal structures in odontocetes), as offered by Cranford et al. (1996), indicates that sperm whales are closely allied to the other
odontocetes. Therefore, it would seem that whatever sound generation
mechanism is at work in sperm whales should apply to all toothed whales.
Norris and Harvey (1972) published a description of the peculiar hypertrophied anatomy of the sperm whale nose and ascribed to it a sound generation function. Norris and Harvey proposed that the unique pulse packets
emitted by sperm whales (Goold 1996) originated from the museau de singe,
a valvular structure situated at the front of the head just beneath the whale's
blowhole (Pouchet and Beauregard 1885). Norris and Harvey proposed
that the primary pulse, once generated, propagated forward directly into
the environment from the museau, and that some residual acoustic energy
reverberated within the spermaceti organ and leaked into the environment
with each reverberation cycle.
Norris later amended the original proposal to suggest that sounds travel
immediately backwards from the museau, through the spermaceti organ,
off an acoustically reflective frontal air sac covering the paraboloid face of
the skull, then forward through the lenslike structures of the junk and finally
into the aquatic environment (Cranford 1999). No evidence can currently
distinguish between the validity of these competing notions. Unfortunately,
Norris and Harvey's paper received very little attention when it was published, most likely because the photographs were so poorly reproduced that
they were incomprehensible. In retrospect, Norris and Harvey's paper was
seminal because it described the site of sound generation and the basic
mechanism, as we now understand it operates in all odontocetes.
Schenkkan and Purves (1973) also studied the anatomy of the sperm
whale nose. They attempted to put the anatomy of the sperm whale's peculiar nose in the context of other odontocetes by making comparisons
between a fetal sperm whale, a pygmy sperm whale (Kogia breviceps) and
a Hector's dolphin (Cephalorhynchus hectori). Although their anatomic
work was carefully conducted, they ultimately concluded that the larynx
must be the site of sound generation.
It is important to point out that Schenkkan and Purves did not arrive at
their conclusion because of any convincing evidence in favor of laryngeal
phonation. Their conclusion was based primarily upon negative evidence.
None of the objections they raised directly discounted the nasal phonation
hypothesis. On the other hand, it is possible to understand why Schenkkan
and Purves concluded as they did. They cast serious doubt on the specific
and popular proposal of Evans and Prescott (1962), that the nasal plug
nodes were the sonar signal sources, because those structures were not
123
resulting in perhaps the largest and most complex nose in the animal
kingdom (Cranford 1999). These facts have caused some misconceptions
and controversy in the attempts to understand sound generation by comparing the anatomic relationships between nasal apparatuses in physeterid
and nonphyseterid odontocetes. The interpretation of these homologous
relationships (between nasal structures in odontocetes), as offered by Cranford et al. (1996), indicates that sperm whales are closely allied to the other
odontocetes. Therefore, it would seem that whatever sound generation
mechanism is at work in sperm whales should apply to all toothed whales.
Norris and Harvey (1972) published a description of the peculiar hypertrophied anatomy of the sperm whale nose and ascribed to it a sound generation function. Norris and Harvey proposed that the unique pulse packets
emitted by sperm whales (Goold 1996) originated from the museau de singe,
a valvular structure situated at the front of the head just beneath the whale's
blowhole (Pouchet and Beauregard 1885). Norris and Harvey proposed
that the primary pulse, once generated, propagated forward directly into
the environment from the museau, and that some residual acoustic energy
reverberated within the spermaceti organ and leaked into the environment
with each reverberation cycle.
Norris later amended the original proposal to suggest that sounds travel
immediately backwards from the museau, through the spermaceti organ,
off an acoustically reflective frontal air sac covering the paraboloid face of
the skull, then forward through the lenslike structures of the junk and finally
into the aquatic environment (Cranford 1999). No evidence can currently
distinguish between the validity of these competing notions. Unfortunately,
Norris and Harvey's paper received very little attention when it was published, most likely because the photographs were so poorly reproduced that
they were incomprehensible. In retrospect, Norris and Harvey's paper was
seminal because it described the site of sound generation and the basic
mechanism, as we now understand it operates in all odontocetes.
Schenkkan and Purves (1973) also studied the anatomy of the sperm
whale nose. They attempted to put the anatomy of the sperm whale's peculiar nose in the context of other odontocetes by making comparisons
between a fetal sperm whale, a pygmy sperm whale (Kogia breviceps) and
a Hector's dolphin (Cephalorhynchus hectori). Although their anatomic
work was carefully conducted, they ultimately concluded that the larynx
must be the site of sound generation.
It is important to point out that Schenkkan and Purves did not arrive at
their conclusion because of any convincing evidence in favor of laryngeal
phonation. Their conclusion was based primarily upon negative evidence.
None of the objections they raised directly discounted the nasal phonation
hypothesis. On the other hand, it is possible to understand why Schenkkan
and Purves concluded as they did. They cast serious doubt on the specific
and popular proposal of Evans and Prescott (1962), that the nasal plug
nodes were the sonar signal sources, because those structures were not